Abstract: Observing the dynamic histopathology change of the mice brain and the cyst formation after the mice infected by toxoplasma gondii prugniaud strain. 40 ICR mice were infected intraperitoneally with cysts,and a mouse was got 10 cysts(0.5mL). 22 mice were injected PBS partes aequales. Incidence of the mice was observed. The mice were put to death,and the brains were detected by using histopathology and immunohistochemistry,and extracting DNA of brain tissue,and then amplifying the special sequence of toxoplasma gondii B1 gene by PCR at 5-day(5d),10d,15d,20d,25d,30d,60d,90d,120d,150d and 180d post-infection. The results showed that the mice infected with the cysts began to fall ill at 6d post-infection,and to recover at 20d post-infection. Symptoms contained decreased food appetite,lofty fur,sloth,buffeting and diarrhea,and the mortality rate was 15 percent. Microscopic examination from HE staining didn’t find obvious histopathology changes at 5d post-infection. Neuronal degeneration,satellitosis and neruonophagia were found since 10d post-infection. We found some neuroglial cell tubercle and a small toxoplasma gondii cyst since 15d post-infection. Inflammatory cells infiltration can be seen on cavitas subarachnoidealis since 20d post-infection. Sleeve cuffing can be seen since 25d post-infection. Granulation tissue can be seen on cavitas subarachnoidealis at 90d post-infection. Cysts,neuroglial cell tubercle and lesser inflammatory cell infiltration on cavitas subarachnoidealis would coexist from 120d to 180d post-infection. Toxoplasma gondii or Toxoplasma antigen particle could be seen in endochylema or nucleus of brain tissue since 10d post-infection by immunohistochemistry,and then cyst began to increase with antigen began to decrease. Specificity sequence of Toxoplasma gondii B1 gene could be detected by PCR from 10 days to 180 days post-infection. Those results indicated that tachyzoite of toxoplasma gondii prugniaud strain would invade the brain after several days post-infection,but the cyst would be found until 15 days post-infection. The strain could lead to some pathology changes,including degeneration and necrosis of brain cells,and non-specificity meningoencephalitis. Pathological changes would to relieve gradually with the cyst formation after 15d post-infection,but the cyst would exist the brain until 180d post-infection.